YAY kitty! This doesn't look too difficult, but I'd still prefer to leave the sculpting to you than doing it myself. When you do a tutorial, you can't prevent that some people might copy your techniques, though...

Processes of production cannot be copyrighted, so if someone makes their own gourd kitty using your tutorial, they have every right to sell it. The only thing about this that's copyrighted is the tutorial itself (the images, the text, and the arrangement of them), so people cannot take this tutorial and sell it or parts of it (or do much of anything with it without your permission, aside from read it and follow it).

If you want legal protection for a technique, you have to patent it (unlike copyright, patents are not automatic, and are very expensive to obtain).

You are welcome to ask people not to sell sculptures made this way, but ultimately it's their choice whether to obey your wishes or not, and they would not be committing copyright infringement if they choose not to obey.

I realize you probably didn't want to hear this, but I think it's important for people to understand basic copyright stuff, including when copyright doesn't apply.